This invention relates generally to apparatus for joining materials as by spot welding, brazing or soldering, and more particular to apparatus for joining materials using a laser beam.
Although materials joining processes such as spot welding, brazing, or soldering are well known and are used extensively for joining parts including electrical components, it has been difficult to apply such joining processes to the microelectronics industry for joining small microelectronic parts. One reason has been the difficulties in precisely controlling the power applied to the parts and in confining the heating to a localized region of the parts so that the parts are joined without damage to the parts or to other materials or components in their vicinity.
Normal brazing and soldering processes require that an electrode which has been resistance heated be brought into mechanical contact with the parts and held in contact with the parts long enough to enable sufficient heat to be transferred by conduction to effect joining. With a heated electrode, it is very difficult to confine the heating to a localized area or to control the amount of heat which is transferred to components in the vicinity of the electrode, particularly when the parts being joined are located in a confined area. In a resistance spot welding process, a split electrode, as of copper, is frequently used to pass electrical current through two parts which are held in mechanical contact with one another. The current produces resistance heating and joins the parts. As with brazing and soldering, it is difficult in a spot welding process to control precisely the amount of heating or to confine the heat affected area of the parts sufficiently to avoid damage.
Apparatus employing laser beams are known for performing various material treating processes such as cutting, drilling, welding, brazing, marking, or localized heat treating. Typical of these apparatus are those disclosed in commonly assigned U.S. Pat. Nos. 4,564,736, 4,676,586, and 4,681,396 wherein an optical fiber is employed for transmitting a laser beam from a remote source to a processing region of a workpiece. In these apparatus, the output end of the optical fiber is supported in an output coupler adjacent to the workpiece. The output coupler includes a lens system for focusing the diverging laser beam emitted from the end of the optical fiber to a small spot on the workpiece. The output coupler does not contact the workpiece, but is merely used for focusing the laser energy onto the workpiece. Thus, the apparatus and processes disclosed in the parents are non-contact ones, which is generally true of other known laser materials processes, such as laser welding. Although laser processes can be precisely controlled so as to provide a desired localized deposition of high energy, the absence of mechanical contact between the tool which supplies the laser beam and a workpiece is disadvantageous in laser joining processes such as laser welding, since it requires that external positioning devices or fixtures be employed to hold two workpieces to be joined in mechanical contact. This may render automation of the joining process difficult and inconvenient. Moreover, in some applications, as, for example, where it is necessary to join parts which are located in a confined space, it is impractical to employ external positioning devices or fixtures to hold the parts together, and this may preclude joining the parts using a laser process.
It is desirable to afford a fiber optic laser joining apparatus which voids the foregoing and other problems of known laser joining apparatus, and which facilitates the joining of microelectronic components reliably, rapidly, and without damage to the components or to other components in their vicinity. It is to these ends that the present invention is directed.